Conventionally, optical components, such as lenses, mounted in optical devices have been formed of a glass, plastic, single crystal, or ceramic.
In recent years, optical materials with a high Abbe number have been demanded. An optical material with a high Abbe number is advantageous in terms of chromatic aberration correction or spherical aberration correction, when used particularly as a lens material for an imaging optical instrument handling a wide wavelength range of visible light, e.g., an imaging optical instrument, such as a camera or a video camera.
As a common optical material, a single crystal containing yttrium-aluminum-garnet (hereinafter referred to as “YAG”) is known from Patent Document 1.
However, since a single crystal has the problems of high manufacturing cost and low productivity, an optical material containing a ceramic (hereinafter “polycrystal” material is referred to as “ceramic”) has been desired.
Patent Document 2 discloses a translucent ceramic containing a Ba(Mg, Ta)O3 perovskite as a main component. In such a material, optical properties, such as a refractive index and an Abbe number, can be changed by substituting a part of Mg and/or Ta with Sn and/or Zr. However, the Abbe number of such a material, is also insufficient.
Then, an attempt has been made to produce an optical material containing YAG with a high Abbe number using a ceramic, and is disclosed in Patent Document 3.
However, the YAG ceramic disclosed in Patent Document 3 requires calcination in vacuum or calcination in a reducing atmosphere to obtain translucency. Therefore, the YAG ceramic disclosed in Patent Document 3 has problems in that the manufacturing cost is high and it is difficult to obtain stable properties.
Moreover, the YAG ceramic disclosed in Patent Document 3 has problems in that optical properties, such as an Abbe number and a refractive index, are difficult to adjust in a wide range, resulting in reduced degree of freedom in design of an optical component or an optical device.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 6-135800
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-75512
Patent Document 3: Japanese Unexamined Patent Application Publication No. 6-107456